1. Field of the Invention
This invention relates to a method of treating wood to increase its fire and rot retardancy characteristics.
2. Description of the Prior Art
In many environments it is very desireable to minimize the susceptibility of wood to fire and/or rot. Both of these potentially damaging characteristics of wood are particularly prevalent in the mining field where wooden supports and framing members are continuously exposed to the dangers of fire and rot. The early U.S. Pat. No. 35,811 (Lapparent) recognizes that virgin wood may be surface charred to reduce its normal tendency to decay and rot. To achieve its charred layer Lapparent has its wood exposed to jet burners and thus in contact with opened flames. In the U.S. Pat. No. 1,009,436 (Partridge et al) a board is placed inside a chamber which is heated by a series of burners outside of the chamber. Heating of the chamber takes place until . . . "the surface of the board takes fire and burns evenly throughout its entire surface while passing through the chamber." (page 2, lines 39-41). The Schmid U.S. Pat. No. (1,758,336) discloses a board being passed between two oscillating torches to char its surface with brushes afterwards being used to remove the charred surface. With these three methods, flaming combustion of the wood occurs which means the charring process is governed by the heat flux from the flame on the wood surface as well as from the external heat sources of burners and torches. This form of heat flux is difficult to control--as would be the directly apply heat from any external torches or burners--; more likely to burn away the char-layer to produce ash; has little likelihood of producing a uniform char-layer; and may partially decompose the wood below the char-layer to detract from the wood's strength without adding any corresponding fire retardancy benefit.
The prior art also discloses--U.S. Pat. No. 18,828 to Tenney et al.--the use of a heated roller to char wood to increase the wood's fire and rot retardancy. With this method flaming combustion, with all of its mentioned drawbacks could occur; if the temperature of the hot roller was sufficiently high. If the temperature of the wood roller contact surface were kept sufficiently low to avoid flaming combustion, the time required to form the minimum depth char-layer (3 mm) found acceptable by us would according to our calculations be about three times greater. Further, since the roller's contact surface is flat--as contrasted against the high surface radiant heat flux we employ--it is limited mainly to flat wood surfaces whereas we can accommodate various contours and shapes. One additional advantage in using radiant energy over a contact heat source is the lack of pressure on the char-layer surface, such pressure being capable of damaging the structural integrity of the wood.